Unidirectional device having means for transmitting only one sense of a circularly polarized wave



Nov. 15, 1966 GREMlLLET 3,286,203

UNIDIRECTIONAL DEVICE HAVING MEANS FOR TRANSMITTING ONLY ONE SENSE OF A GIRCULARLY POLARIZED WAVE Filed Aug. 5, 1963 MAGNETC FIELD CIRCULA RLY POLARIZED 2 1 WAVE QIQCULAR WAVE emoe SEMI QO|\JDLJCTOR DISC United StatesPat-ent 3,286,203 UNIDIRECTIONAL DEVICE HAVING MEANS FOR TRANSMITTING ONLY ONE SENSE OF A CIR- CULARLY POLARIZED WAVE Jacques Gremillet, Paris, France, assignor to CSF-Compagnie Generale de Telegraphic Sans Fil, a corporation of France Filed Aug. 5, 1963, Ser. No. 299,988 Claims priority, application France, Aug. 10, 1962,

906,672 4 Claims. (Cl. 33324) The present invention relates to systems for the unidirectional transmission of electromagnetic waves. More particularly it relates to the propagation of a circularly polarized wave through a plate of conducting or, preferably semi-conducting material, which is arranged transversely of the transmission direction and is subjected to a longitudinal continuous magnetic field.

The applicant has discovered that, when the frequencyof the incident wave is much less than the cyclotron resonance frequency and at the same time, the electron collision time is much .greater than the reciprocal of the cyclotron resonance angular frequency, the incident wave i transmitted with relatively low loss when the circular polarization rotates in the same direction as the electrons, and, on the contrary, is practically not propagated when the circular polarization is in a direction opposite to that of the electrons under the action of the magnetic field.

The unidirectional arrangement according to the invention includes means for transmitting a guided wave with an essentially circular polarization, a plate of conducting, or preferably semi-conducting, material, placed transversely of the transmission direction and means for applying to this plate a longitudinal continuous magnetic field.

The single figure of the appended drawing shows very schematically, such an arrangement. The arrangement shown comprises a circular waveguide 1, a semiconductor disc 2 perpendicular to the waveguide axis, and means for providing a longitudinal continuous magnetic field H.

By way of example, disc 2 may be of indium antimonide and 2.7 mm. thick, with an impurity concentration such that it contains electrons per cm. The circularly polarized wave may have, for example, a frequency of 10 c./ s.

When the arrangement is operated at the temperature of liquid nitrogen, for a magnetic field of 10,000 gauss, directed in a direction such that polarization vector rotates in the same direction as the electrons, the power transmitted is a maximum.

The arrangement can also be operated at ordinary temperature: in this case, other things being equal, the power transmitted is a maximum when the thickness of the disc is 0.2 mm., but losses are about ten times greater than at the temperature of liquid nitrogen.

If either the direction of rotation of the polarization of the incident wave, or the direction of the magnetic field, is reversed, the wave is not propagated.

This phenomenon can be explained by a change of sign of the real part of the complex dielectric constant of the material when H changes sign.

As regards the practical aspect of the phenomenon, there is a certain analogy with the gyromagnetic effect observed in ferrites, but, in the latter case, the magnetic 3,286,203 Patented Nov. 15,1966

field acts on the permeability of the material and not on its dielectric constant.

An important advantage of the unidirectional device described consists in the fact that it can be operated both at very-low frequencies and at frequencies of several tens of thousands of mc./s.

In order that the device may operate, the frequency of the incident wave has to be substantially less than the cyclotron resonance frequency. If such is not the case, the electrons rotate at the same velocity as the electric field of the incident wave and the latter is not transmitted. But the cyclotron resonance frequency, for example in the case of indium antimonide, may be of the order of i0 c./s., so that the upper operating frequency limit of the device is in practice very high. This frequency has no lower theoretical limit.

The choice of the material for the plate takes into account the second requirement for the device to operate, i.e., a collision time substantially greater than the reciprocal of the resonance angular frequency. This re quirement means that the electrons must have the time necessary to make at least one revolution during the average time interval between two successive collisions.

For relatively low operating frequencies, this requires a long collision time, as is the case with certain semiconductors, metals and semi-metals.

It is to be understood that the arrangement described and shown is in no way restrictive: a guided wave with an essentially circular polarization may be used which is generated by any appropriate means according to the particular frequencies desired.

What is claimed is:

1. A unidirectional transmission device circularly polarized for Waves having a given frequency comprising a circular waveguide portion, means for generating in said guide portion a direct-current magnetic field extending along the axis thereof and a wall of a semiconductor material having a cyclotron resonance frequency higher than said given frequency and an electron collision time higher than the reciprocal of the cyclotron resonance angular frequency, said wall extending normally to said axis over the whole cross-section of said guide.

2. An unidirectional transmission arrangement comprising: means having a cross-section for transmitting a guided circularly polarized high frequency Wave propagating in a predetermined direction, means for applying to said transmitting means a steady magnetic field parallel to said predetermined direction, a body contained in and extending over the whole of said cross-section of said transmitting means normally to said direction, said body being made of a material having free carriers and a cyclotron resonance angular frequency for said magnetic field substantially higher than the angular frequency of the wave and an electron collision time substantially higher than the reciprocal of said angular cyclotron frequency.

3. An unidirectional transmission arrangement as claimed in claim 2, wherein said material is a semi conductor.

4. An unidirectional transmission device comprising a circular wave guide portion for propagating a circularly polarized wave, means for generating in said guide portion a steady magnetic field extending along the axis thereof, and a wall extending normally to said axis over the whole cross section of the guide, said wall being 3 v a v 4 made of a material having free carriers, and a'cyclotron 3,121,203 2/1964 Heywang. a ar frequency for s n drma netiaafield.substantially. REFERENCES 4 higher than the reciprocal of said angular frequency, and an electron collision time substantially higher than the reciprocal of said angular cyclotron frequency. 5

Barlow et al.: Microwave Hall Effect and the Accompanying Rotation of the Plane of Polarization, Proc. of the IEE, February 1961, pp. 349-353.

References Cited by the Examiner UNITED STATES PATENTS 2,644,930 7/1953 Luhrs et -al. 333l.1

HERMAN KARL SAALBACH, Primary Examiner.

P. L. GENSLER, Assistant Examiner. 

2. AN UNIDIRECTIONAL TRANSMISSION ARRANGEMENT COMPRISING: MEANS HAVING A CROSS-SECTION FOR TRANSMITTING A GUIDED CIRCULARLY POLARIZED HIGH FREQUENCY WAVE PROPAGATING IN A PREDETERMINED DIRECTION, MEANS FOR APPLYING TO SAID TRANSMITTING MEANS A STEADY MAGNETIC FIELD PARALLEL TO SAID PREDETERMINED DIRECTION, A BODY CONTAINED IN AND EXTENDING OVER THE WHOLE OF SAID CROSS-SECTION OF SAID TRANSMITTING MEANS NORMALLY TO SAID DIRECTION, SAID BODY BEING MADE OF A MATERIAL HAVING FREE CARRIERS AND 